Replace the inside of a PS1 Namco light gun with a microcontroller with HID support and turn into a light gun/mouse.
Interacting with Atlas Scientific sensors over USB.
Replace all your remote controls with your phone and Arduino.
Simulate a NeoPixel matrix of any size up to 40 x 35. It contains most of the Adafruit GFX functions and can even draw bitmaps!
Tired of only being able to test pixel patterns on actual NeoPixels? Now you can use Python to view your changes and make tweaks!